1. Field of the Invention
The present invention relates to a process and system to convert thermal energy from low temperature sources, especially from low temperature geothermal fluids, into mechanical and/or electrical energy.
More particularly, the present invention relates to a process and system to convert thermal energy from moderately low temperature sources, especially from geothermal fluids, into mechanical and electrical energy, where a working fluid comprises a mixture of at least two components, with the preferred working fluid comprising a water-ammonia mixture. The present invention also relates to a novel thermodynamic cycle or process and a system to implement it.
2. Description of the Related Art
Prior art methods and systems for converting heat into useful energy are well documented in the art. In fact, many such methods and systems have been invented and patented by the inventor. These prior art systems include U.S. Pat. Nos.: 4,346,561, 4,489,563, 4,548,043, 4,586,340, 4,604,867, 4,674,285, 4,732,005, 4,763,480, 4,899,545, 4,982,568, 5,029,444, 5,095,708, 5,440,882, 5,450,821, 5,572,871, 5,588,298, 5,603,218, 5,649,426, 5,822,990, 5,950,433 and 5,953,918; Foreign References: JP 94815 B2 and Journal References: NEDO Brochure, xe2x80x9cECO-Energy City Projectxe2x80x9d, 1994 and NEDO Report published 1996, pp. 4-6, 4-7, 4-43, 4-63, 4-53, incorporated herein by reference.
Although all of these prior art systems and methods relate to the conversion of thermal energy into other more useful forms of energy from moderately low temperature sources, all suffer from certain inefficiencies. Thus, there is a need in the art for an improved system and method for converting thermal energy from moderately low temperature sources to more useful forms of energy, especially for converting geothermal energy from moderately low temperature geothermal streams into more useful forms of energy.
The present invention provides a method for implementing a thermodynamic cycle comprising the steps of expanding a gaseous working stream, transforming its energy into usable form and producing a spent stream. After expansion and work extraction, the spent stream is mixed with at least one lean stream to form a lean spent stream. The lean spent stream is then used to heat a liquid first working stream to form a heated first working stream and a pre-condensed stream which is then condensed to form a liquid stream. The liquid stream is then mixed with an enriched stream to formn the liquid first working stream. A portion of this stream is then depressurized to an intermediate pressure and separated into an enriched vapor stream and the lean stream; while a second portion of the liquid first working stream is heated to form the gaseous working stream.
The present invention provides a method for implementing a thermodynamic cycle comprising the steps of expanding a gaseous second working stream, transforming its energy into usable form and producing a low pressure spent stream. After expansion, the spent stream is mixed with a first lean stream forming a lean spent stream. Heat is then transferred from this stream to a first working solution to form a heated first working solution. The cooled lean spent stream is then mixed with a second lean stream to form a pre-condensed stream, which is then condensed to form a liquid stream. The liquid stream is then mixed with a first enriched vapor stream to form the first working solution. A first portion of the heated first working stream is separated into a second enriched vapor stream and the second lean stream. A second portion of the heated first working stream is then heated with an external heat source fluid stream to form a partially vaporized first working stream. The partially vaporized first working stream is then separated into a fourth enriched stream and a third lean stream. A first portion of the third lean stream is then separated into the first lean stream and a third enriched stream and the third enriched stream is mixed with the second enriched stream to form the first enriched stream. A second portion of the third lean stream is mixed with the fourth enriched stream to form the second working stream, which is then fully vaporized to from the gaseous second working stream.